With the recent rapid increase in the cost of energy, attention has been focused on the need to conserve natural resources by reducing wasteful and needless consumption of energy. Environmental heating and cooling systems are significant consumers of energy and thus are significant targets for energy conservation. To this end, various control systems have been applied to heating and cooling systems to reduce their energy consumption and increase their overall operating efficiency.
One type of prior art control system simply turns off the heating or cooling system when the associated environment is unoccupied. The turning off and subsequent turning on of the system may be controlled manually or automatically--for example, by a clock if the usage pattern of the environment is well-established and regular. This type of "on-off" control system is unsatisfactory for a number of reasons. First, it permits excessive temperature variations in the environment and these excessive variations may impose an excessive load on the heating or cooling system when it is turned on. Also, it is inappropriate for use in environments wherein excessive temperature variations may cause damage to equipment therein. Further, there may be considerable delays in the area reaching the desired temperature when the system is turned on after it has been off for a considerable period of time. Decreases in fuel consumption will be highly dependent on the extent of the temperature variations experienced and under certain conditions, it is even possible to increase fuel consumption.
A more advanced control system couples a multi-setting thermostat with a clock, with the set point of the thermostat being selected by the clock. For example, in domestic systems of this type two temperature set points may be provided, one for daytime use and another for nightime use. The multi-setting, clock-driven thermostat is an improvement over the "on-off" system in terms of providing a fixed temperature range. However, efficiency still is sacrificed because at times the thermostat may be set by the clock to a higher or lower temperature than is necessary, taking into account the use of the room. Also, when uses are made of the area other than as normally programmed into the clock, the room will not be at the temperature desired for that use.